I wish Moffat hadn't named her that "-_- It's a surname, nothing else.
I don't really have a problem with the name in theory (I'm not a fan of surnames on girls but they're so rampant that I might as well get used to it) but I do think that Oswin will be very tied to Doctor Who, simply because it was so unheard of as a fn before the character.
ETA: I don't have many other associations with the name, other than it kind of reminds me of Oswald, so then there's Oswald Mosley and Oswald the Octopus...
I think the Mary Sue bit is lulling us into a false sense of security. Something is up with this one. Something sketchy. I don't think she's like Amy, though. I think she's pretty timid in comparison to Amy, and really in comparison to any of the others.
Also, I think Oswin is going to be pretty tied to the character, but not everyone is into Doctor Who, so there is that.
It's not a very pretty name. When I see it all I can see is O'swine. It makes me think of pigs and muck and it's just not a pretty picture.
I don't have the Doctor Who association.
I wouldn't use it as a name at all... but it seems more masculine than feminine (I'm a Doctor Who fan, but trying to put in perspective of someone who isn't)
I don't know the Dr. Who reference but Oswin doesn't strike me as an attractive name. It also sounds more masculine than feminine.